Stool



FIG. 1 is a front perspective view from above of an ornamental design for a stool showing my new design;

FIG. 2 is a front orthographic view thereof;

FIG. 3 is a rear orthographic view thereof;

FIG. 4 is a left side orthographic view thereof;

FIG. 5 is a right side orthographic view thereof;

FIG. 6 is a top orthographic view thereof; and,

FIG. 7 is a bottom orthographic view thereof.

The dashed lines shown in FIG. 7 are included for the purpose of illustrating environmental subject matter only and form no part of the claimed design. 

The ornamental design for a stool, as shown and described. 